As is well known, a solenoid assembly consists essentially of a coil of wire or winding that is wrapped around a hollow bobbin. An enclosure or frame made of a magnetically conductive material normally contains the coil. An actuator or plunger moves back and forth within a passageway formed in the bobbin. Application of electrical power to the coil will move the plunger between an energized, latched position and a de-energized, unlatched position. A return spring is provided to assist movement of the plunger back to the unlatched position. Typically, the plunger is designed with some sort of feature which allows users to connect whatever structure they would need to actuate with it. At one end of the solenoid assembly in the passageway of the bobbin and rigidly attached to the frame is a slug of magnetic material known as a backstop. The backstop establishes the maximum pulling distance the plunger can achieve when the coil is energized by electrical power. The coil is normally wound to parameters that will dictate the amount of electromagnetic forces placed upon the plunger based upon a desired application.
When a solenoid coil is momentarily energized, the electromagnetic energy causes the plunger to move towards the backstop into the latched position compressing the return spring. As the plunger approaches the backstop, its level of force generally increases. When the plunger impacts and bottoms out on the backstop, the maximum amount of pulling power is achieved. In a magnetic latching solenoid, power to the coil is removed and a set of permanent magnets in the frame is used to hold the plunger in its latched position. When it is desired to move the plunger to an unlatched position, the solenoid coil is momentarily energized to overcome the force of the permanent magnets after which release of the compressed spring force completes the return movement of the plunger.
In certain high wattage applications when the solenoid is moved to the latched position, the plunger imposes a large impact loading upon the rigidly connected backstop. Upon repeated use, this impact loading deforms the plunger such that movement of the plunger is impaired leading to the failure in the solenoid performance.
Accordingly, it is desirable to provide a solenoid assembly which avoids failures due to destructive impact loading between the plunger and backstop. More specifically, it is desirable to provide the solenoid assembly with a modified connection between the backstop and the frame, and position a shock absorbing element between the backstop and the frame to prevent damage to the plunger over repeated cycles of use and extend the service life of the solenoid assembly.